More than half of pools in a new U.S. study showed signs of fecal contamination. / Patrick Seeger, AFP/Getty Images

by Kim Painter, Special for USA TODAY

by Kim Painter, Special for USA TODAY

Here's a good reason never to swallow water from a swimming pool: A new study found telltale signs of feces in more than half of pools sampled in Atlanta last summer.

The problem is not confined to Atlanta, says Michele Hlavsa, a researcher who promotes healthy swimming at the federal Centers for Disease Control and Prevention: "I think if we had done this study anywhere in the United States, we would have found the same thing."

And it's not the fault of pool operators, Hlavsa says: "This is really about swimmer hygiene."

In other words: there's poop in our pools because people are not taking showers before swimming or are having accidents in the water. And public health officials care because sometimes that contaminated water makes people very sick.

For the study, published Thursday in the CDC's Morbidity and Mortality Weekly Report, Hlavsa and colleagues tested water from filters at 161 pools, including 37 municipal pools, 89 club or membership facilities and 35 small water parks (which included any facility with so much as a spray feature, Hlavsa says).

They found DNA from E. coli bacteria, normally found in the human gut and feces, in 58% of samples. That's a "fecal indicator," or proof that poop has rinsed off someone's bottom or been deposited directly into the water, the report says. The tests did not indicate whether the bacteria were alive or dead.

Municipal pools were more likely than other pools to show signs of fecal contamination.

The good news: none of the E. coli was the toxic, illness-causing O157:H7 strain. Researchers also were reassured that signs of cryptosporidium and giardia, germs that spread through feces and cause diarrhea, were found in just one and two samples, respectively.

It's worth noting that Atlanta reported no outbreaks of water-borne illnesses in pools in 2012. But public health officials are concerned that the overall rate of such illnesses has increased in the United States in recent years.

Here's what the CDC recommends swimmers do to stay healthy and keep others healthy â?? whether swimming in a pool, lake, river or ocean (or using a hot tub):

-- Stay out of swimming water when you have diarrhea.

-- Shower with soap before swimming.

-- Take children for bathroom breaks every 60 minutes.

-- Wash your hands with soap after using the toilet or changing diapers.

-- Avoid changing diapers next to the pool.

-- Avoid swallowing the water.

CDC says that properly maintaining pools, with appropriate chlorine and pH levels, can go a long way toward preventing illness from the germs that get into the water. But swimmers can't count on 100% protection, Hlavsa says: "You have to take some responsibility."